Conventionally, there is widely used a compact disc (CD) in which the sampling frequency fs is about 44.1 kHz and the PCM method is used to record one sample as 16-bit digital audio data for each channel. There has been proposed a so-called super audio compact disc (SACD) in which 1-bit audio stream data is recorded with a very high sampling frequency generated by the DSD (direct stream digital) method, for example, a frequency 64 times higher than the sampling frequency fs in the ordinary CD.
By oversampling delta-sigma modulation of an input signal with 64fs, there is generated a 1-bit audio digital signal. Hereupon, the 1-bit audio digital signal is decimated into a multi-bit PCM code in the CD using the PCM method. In the SACD using the DSD method, however, the 1-bit audio digital signal is recorded directly to the SACD.
The frequency band of the 1-bit audio signal recorded to the SACD is about 100 kHz. This is rather wider than the frequency band of the signal in the PCM method adopted in the CD.
In the PCM method, one sample is taken as 16-bit digital audio data for each channel, such as digital audio data defined in IEC 60958 or the like. In such digital audio data, “0” data is used as a signal indicating a muting.
On the other hand, the 1-bit audio signal in the DSD method uses a special mute pattern data called so-called “9-6 pattern” of “10010110” as a signal indicative of a muting. When music data is changed over to a 9-6 pattern or vice versa, a noise will possible occur unless the music data and 9-6 pattern are put in phase with each other at the changeover point.
In a system including a medium player and amplifier in combination, muting can be applied at the signal changeover point inside the system by detecting a trigger for a signal changeover, for example, an operation for play by the user.
In a system including separate unit components such as 1-bit audio signal player and amplifier, a trigger generated in the player cannot be detected at the amplifier and thus the amplifier cannot apply muting at any signal changeover point. That is, the amplifier converts a signal sent from the player into an analog signal and delivers it as it is without applying any muting at the point of changeover point between a muting (9-6 pattern) and music data. If the muting and music data are out of phase at the changeover point, a noise, if any, will be delivered as it is. Therefore, the noise will possibly be heard at the start of playing a signal and during shift from the signal playing to stop of the playing.